Differential changes in junctional complex proteins suggest the ependymal lining as the main source of leukocyte infiltration into ventricles in murine neurocysticercosis

Abstract

The blood brain barrier (BBB) and the blood-cerebrospinal fluid barrier (BCB) limit the influx of immune mediators and bloodstream compounds into the central nervous system (CNS). Upon injury or infection, the integrity of these barriers is compromised and leukocyte infiltration occurs. The BCB is located in the choroid plexuses (CPs) found within ventricles of the brain, and it is considered one of the main routes of cellular infiltration into the CNS into healthy individuals. Our group recently showed that in a murine model of neurocysticercosis (NCC), there is a moderate increase in infiltration of leukocytes into ventricles, but the BCB is hardly compromised. To elucidate the role played by CPs and surrounding ependyma in leukocyte infiltration at ventricular sites, we analyzed changes in the expression of junctional complex proteins in animals intracranially infected with Mesocestoides corti. The results indicate that infection does not change the expression pattern of junctional complex proteins in CPs, but structural alterations and disappearance of these proteins were evident in ependyma adjacent to the internal leptomeninges. The kinetics and magnitude of these changes directly correlated with the extent of leukocyte infiltration through ependyma and with the expression and activity of MMPs. The results of this study indicate that the anatomical elements of the BCB are minimally disrupted during the course of murine NCC. Thus, most of the leukocytes infiltrating ventricles appear to extravasate through pial vessels located in the internal leptomeninges juxtaposed to the ependyma layer and then traverse the ependyma cells. In addition, MMP activity seems to be involved in this process. These results provide evidence for a previously undescribed entry route for leukocytes into the CNS.

Multiple expression of matrix metalloproteinases in murine neurocysticercosis: Implications for leukocyte migration through multiple central nervous system barriers

“…Later post infection times of 3-5 wks showed increasing numbers of leukocytes expressing active MMPs (Table 1). Consistent with our previous results indicating infection-induced breaks in the ependyma as a source of inflammatory infiltrates in ventricles [3], Fig 7F shows large numbers of CD11b + cells (presumably macrophages) that have appeared to cross through the ependymal lining (demarcated by cadherin staining) into the ventricle. Also shown is the active expression of MMP-12 (Fig 7G), MMP-8 (Fig 7H), and MMP-2 ( Fig 7I).…”

“…Leukocyte extravasation through the CPs is relatively low during murine NCC [2,3]. Of the cells that appear to be exiting the CPs, expression of MMP-12 ( Fig 7C) and MMP-16 was found mainly exhibiting collagen activity, and to a lesser extent MMP-3 exhibiting gelatin cleavage.…”

“…Our studies in a mouse model of NCC have revealed differential breakdown of the BBB and the blood-cerebrospinal fluid barrier (BCB) dependant upon the vascular bed, accumulation of blood derived leukocytes, production of inflammatory cytokines and differential expression of MMP-9 [2][3][4]. Many of these pathophysiological conditions have been described in other CNS disorders, and MMPs have been linked to associated mechanisms [28,43,63].…”

“…In fact, this is the normal entry point in the uninfected brain. We have recently shown that leukocytes predominately access the ventricles during infection by disruption of pial vessels in the subependymal area followed by migration of leukocytes into ventricles through a compromised ependymal lining, the epithelial layer that surrounds the ventricle [3]. Therefore, we evaluated the expression and activity of MMPs to assess their involvement in leukocyte migration into ventricles.…”

“…Particular emphasis was given to the expression of MMPs in leukocytes extravasating different types of vasculature as the kinetics of infiltration differs among distinct areas of the mouse brain [2][3][4]. Total mRNA isolated from brains after different post infection times was analyzed using a macroarray specific for MMPs.…”